Digital tracer

ABSTRACT

A tracer for use with a profiling machine or the like has a tracer head which is excited with a source of alternating current to produce an output which varies in amplitude and phase in accordance with the direction and magnitude of deflection of the tracer stylus. The a.c. signal from the stylus is converted into a pulse encoded in time to be representative of the direction of stylus deflection. The time position of the pulse is converted into a digital representation of the angle of the stylus deflection, and the sign and cosine of that angle are extracted from memory and separately multiplied by a factor derived from a manually controlled means operative for preselecting a tracing speed in two multipliers, the outputs of which comprise pulse trains each having a separate pulse for each increment of movement along a machine axis. The pulse trains are connected to a conventional motor drive for driving the machine in response to the output of the tracer head.

United States Patent 1191 Sommeria et al.

[ 1 Jan. 15, 1974 DIGITAL TRACER [75] Inventors: Marcel R. Sommeria, Bridgeview,

111.; David I. Schaap, Munster, Ind.

[73] Assignee: Hyper-Loop, Inc., Bridgeview, Ill.

[22] Filed: Dec. 11, 1972 [21] Appl. No.: 313,974

Primary Examiner B. Dobeck v Attorney-Benjamin H. Sherman et a1.

[ 5 7 ABSTRACT A tracer for use with a profiling machine or the like has a tracer head which is excited with a source of alternating current to produce an output which varies in amplitude and phase in accordance with the direction and magnitude of deflection of the tracer stylus. The ac. signal from the stylus is converted into a pulse encoded in time to be representative of the direction of stylus deflection. The time position of the pulse is converted into a digital representation of the angle of the stylus deflection, and the sign and cosine of that angle are extracted from memory and separately multiplied by a factor derived from a manually controlled means operative for preselecting a tracing speed in two multipliers, the outputs of which comprise pulse trains each having a separate pulse for each increment of movement along a machine axis. The pulse trains areconnected to a conventional motor drive for driving the machine in response to the output of the tracer head.

10 Claims, 6 Drawing Figures DIGITAL TRACER BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracer mechanism, and more particularly to such a mechanism which is digital in character and which produces an output consisting of two separate pulse trains for operating a machine drive in two orthogonal directions, in response to the output of a tracer head.

2. The Prior Art In the copending application of Marcel Sommeria, Ser. No. 266,579, filed June 27, 1972 for Digital Regulating Control for Servo System a motor drive is illustrated which is responsive to a train of input pulses corresponding to the desired movement of the machine drive along one axis. Such pulses may be derived from a number of sources, including a tape reader, or the like. It is desirable to provide a tracer mechanism for producing the pulse trains required by the apparatus of the above identified Sommeria application, so that the machine drive can be controlled to bring about the required changes in position between a tool and the work, in accordance with a pattern followed by the stylus of a tracer head.

Tracer heads are well known in which an a.c. output signal is derived from an a.c. input or exciting signal, the magnitude and phase of the output signal being responsive to the direction and magnitude of the stylus deflection. The output of such tracer heads have customarily been manipulated by analog means to provide one or more d.c. voltage levels which are effective in controlling the operation of a servo system. However, such an arrangement suffers from a tendency to drift over relatively long periods of time. That is, the relation between input and output functions is not constant. It is desirable to eliminate such drift and more particularly to employ digital apparatus which is not subject to such drift. It is also desirable to increase the reliability of the apparatus by using integrated circuitry to as great an' extent as possible, and to provide apparatus adapted to select a speed within a wide range of operating speeds, to establish a constant speed of travel of the machine drive, irrespective of the direction of the movement.

SUMMARY OF THE INVENTION It is a principal object of the present invention to pro vide digital apparatus for producing, in response to the output of the conventional tracer head, a plurality of digital pulses for independently controlling the drive of the machine in two orthogonal directions.

Another object of the present invention is to provide such apparatus which is adaptable to the use of integrated circuitry.

A further object of the present invention is to provide apparatus which is adapted to permit manual selection of the speed of travel of the machine drive over a wide range of speeds, and to maintain a constant selected speed irrespective of the direction of travel.

These and other objects and advantages of the present invention will become manifest upon an examination of the following description and the accompanying drawings.

In one embodiment of the present invention there is provided means for producing a time encoded pulse within each cycle of the excitation voltage applied to the tracer head, means for producing a first digital signal in response to the time position during each cycle of such pulse, means for extracting from a storage device at a memory location corresponding to said digital signal, and at a memory location corresponding to a second digital signal related to the first digital signal, third and fourth digital signals representative of the sine and cosine of the angle represented by said first and second digital signals, and means multiplying the repetition rate of a pulse train in accordance with said third and fourth digital signals, said pulse train being selected in response to operation of a manually operable selecting means.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to the accompanying drawings in which:

FIG. 1 is a functional block diagram of a system constructed in accordance with an illustrative embodiment of the present invention;

FIG. 2 is a functional block diagram of a portion of the apparatus illustrated in FIG. 1.

FIG. 3 is a graph illustrating the relation between the direction of stylus deflection and the digital signal produced in response thereto;

FIG. 4 is a graph of sine and cosine functions of a deflection angle; and

FIG. 5 consisting of FIGS. 5A and 5B taken together is a schematic circuit diagram, partly in functional block diagram form of the apparatus of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 a tracing system incorporating the present invention is illustrated. The tracer head 10 is connected to the digital tracer mechanism 12 which produces two outputs on lines 14 and 16, in response to the input from the tracer head 10. The line 14 carries a plurality of pulses corresponding to the desired movement of the machine drive in an X direction, while the line 16 carries a corresponding pulse train directing movement of the machine drive in a Y direction, perpendicular to the X direction. The line 14 is connected to one input of a resolver lock unit 18 which produces an output connected to a servo amplifier 20 which in turn drives a motor 22. A tachometer 24 is connected mechanically to the shaft of the motor 22 and fiirnishes a signal on a line 26 which is connected to a second input of the servo amplifier 20. A resolver 28 is also connected to the shaft of the motor 22 and varies the phase difference between an output of the resolver lock unit 18 on a line 30 and a second input to the resolver lock unit 18 furnished by the resolver 28 over a line 32. The apparatus including the resolver lock unit 18, the servo amplifier 20 and the motor 22, is exactly as described in the aforementioned Sommeria application. An identical system provided for the drive in the Y direction is connected to the line 16, including a motor 34 which is connected to the Y drive of the machine and which is energized in accordance with pulses on the line 16.

The tracer head 10 is energized with a source of an a.c. signal 9 in order to produce the required signal on the line 11. The tracer head 10 is conventional and the signal on the line 11 is an a.c. signal having the same frequency as the signal supplying to the head 10 by the source 9, but shifted in phase by an amount corresponding to the direction of deflection of the stylus of the tracer head 10, and having an amplitude corresponding to the magnitude of such deflection.

The digital tracer mechanism 12 is shown in more detail in FIG. 2. The line 11 leading from the tracer head 10 is connected to a head-to-address converter 36 which converts the phase of the signal on the line 11 to a digital signal which is representative of a memory location or address in a storage device. The output of the converter 36 is provided on a line 38, which is connected to the input of an address counter 40. The address counter 40 is provided with a plurality of output terminals. One group of output terminals is connected via lines 41 to a sine ROM 42, which produces at a series of output terminals a digital signal representative of the sine of the deflection angle. These output terminals are connected via lines 43 to corresponding inputs of an interpolator unit 44, which acts as a digital multiplier to multiply the frequency of a pulse train supplied to an input of interpolator 44 over a line 46. The output is produced on line 48 and represents a pulse train having a pulse repetition rate equal to that on the pulse train input line 46, multiplied by a quantity represented by the digital signals supplied to the inputs of the interpolator 44 from the ROM 42. This quantity is between and 1, so the pulse repetition rate of the pulse train on the output line 48 is always less than that on the input line 46.

Another series of outputs of the address counter 40 are connected over lines 49 to corresponding inputs of a cosine ROM 50, which produces at its outputs a digital quantity representative of the cosine of the deflection angle. This is connected via lines 51 to inputs of an interpolator 52 which, like the interpolator 44, multiplies the pulse repetition frequency of the pulse train appearing on the input line 46 to produce an output pulse train on an output line 54 having a pulse repetition rate equal to that of the pulse train on the line 46, multiplied by a quantity represented by the digital signals supplied by the lines 51. Accordingly, the lines 48 and 54 each provide pulse trains which operate as the inputs to the resolver lock unit 18 for the X drive and the corresponding resolver lock unit for the Y drive (FIG. 1).

The pulse repetition .rate on the line 46 is derived from a clock unit 56, which furnishes a clock pulses at a constant rate. The clock unit 56 is connected to the input of an interpolator 58, and the line 46 is connected to the output of the interpolator 58. The inputs of the interpolator 58 are connected to a series of switches 60 which are manually operated in accordance with the desired pulse repetition rate of the pulse train for the line 46. The interpolator 58 functions to multiply the pulse repetition rate of the signal produced by the clock source 56 by the quantity represented by the digital signals supplied by the switches 60, so that the pulse repetition rate of the pulse train on the line 46 is the product thereof. The value represented by the setting of the switches 60 is between 0 and 1, so the frequency of the pulses on the output line 46 is always less than the clock frequency.

The frequency of the clock unit 56 is much higher than the frequency of the source 9, and conveniently the source 9 may comprise a frequency divider or the like so that the excitation signal for the tracer head is derived from the output of the clock unit 56.

Referring now to FIG. 3, there is shown adiagramatic illustration of the manner in which a digital signal is generated in response to the deflection angle of the stylus of the tracer head 10. The circle illustrated in FIG. 3 is divided into four quadrants of which the upper right hand quadrant will hereinafter be referred to as quadrant I, with the remaining three quadrants successively designated in counterclockwise rotation as quadrants II, III, and IV. A digitial value between 0 and 127 is generated when the tracer head is deflected in the direction of the first quadrant, a value between 128 and 255 when the deflection is in the second quadrant, a value between 256 and 383 when the deflection is in the third quadrant, and a value between 384 and 511 when the deflection is in the fourth quadrant. It will be appreciated that the 512 discrete digital signals which are generated in response to the direction of tracer deflection can be accommodated by a binary counter having 9 stages, with each of the 512 values being indicated by discrete combination of 9 binary bits. The two most significant bits indicate the quadrant in which the deflection occurs and are illustrated in FIG. 3 for each respective quadrant. In quadrant I the two most significant digits are both Os; in quadrant II the two most significant digits are 01 (with the least significant digit placed on the right hand side), in quadrant III the two most significant digits are 10; and in quadrant IV the two most significant digits are 11. The seven digits of each binary number which occuply the less significant orders proceed in each quadrant from 0 through 127.

It is necessary to extract the sine and cosine of the deflection angle. It is evident from the illustration of FIG. 3 that this can be done with the use of only seven binary bits, which correspond to a single quadrant of deflection, since the remaining two bits identify the quadrant. In FIG. 4 the sine and cosine functions of the first quadrant are represented. For quadrant II, the cosine function is equal to the sine function of quadrant I with the sign reversed, and the sine is equal to the cosine function of quadrant I. For quadrant III the sign of both functions are reversed, and for quadant IV the sine and cosign functions are the same as for quadrant II with the signs reversed. Thus the sine and cosine functions for all four quadrants are derived from data for a single quadrant, requiring only 7 binary bits. The two most significant bits are used to select the appropriate signs for the sine and cosine functions.

Referring now to FIG. 5, there is shown a schematic diagram illustrating the manner in which the sine and cosine functions are extracted. The signal derived from the tracer head 10 is presented to a terminal 62 which is connected through a resistor 64 to one input of a differential amplifier 66 having a feed-back circuit 68 including resistor 67 and capacitor 69. The output of the amplifier 66 is connected through a resistor 70 to the input of a differential amplifier 72 having a feed-back resistor 74.

The output of the amplifier 72 is connected through a resistor 76 to a terminal of a set of double-pole, double-throw reversing contacts 78 and then through a rectifying diode 80 to another terminal of the reversing contacts 78. The contacts 78 are operated by a relay coil 82, connected between a control input terminal 84 and ground, and which is adapted to reverse the polarity of the diode 80 when a control signal is applied to the terminal 84, for reversing the direction of travel of the machine drive relative to the patern being traced by the stylus of the tracer head 10. A capacitor 86 has one end connected through the contact 78 to the diode 80, and its other end connected to ground, and a dc. voltage is produced across the capacitor 86 corresponding to the amplitude of the ac. signal applied to the input terminal 62 from the tracer head 10.

The ungrounded end of the capacitor 86 is connected through a resistor 88 to the input of a differential amplifier 90, which is provided with a feedback resistor 92. The input of the amplifier 90 is also connected via a resistor 94 to the tap of a potentiometer 96, which is connected between a source of positive voltage and ground. Ajustment of the position of the tap of the potentiometer serves to control the level of the signal furnished to the amplifier 90, for the resistors 88 and 94 have the same value, with the result that the level supplied to the input of the amplifier 90 is the average of the rectified voltage appearing across the capacitor 86, and the voltage level selected by means of the potentiometer 96. The potentiometer 96 is adjusted in order to select the desired magnitude of deflection of the stylus of the tracer head 10, which deflection is maintained by the system.

The output of the amplifier 66 is also connected to the input of a differential amplifier 98 through a resistor 100. The amplifier 98 functions as a line receiver to convert the a.c. signal at the output of the amplifier 66 to a square wave, with the vertical portions or transitions of the square wave corresponding to the zero crossing points of the ac. waveform, and having a level which is appropriate for the circuit which is connected to its output. The output of the amplifier 98 is connected to a monostable multivibrator 102, which produces a short, positive going pulse beginning at the positive going transitions of the square wave furnished by the amplifier 98.

The output of the multivibrator 102 is connected to the base of a transistor 104, which has its collector connected through a resistor 106 to a positive source of voltage, and its emitter connected through a resistor 108- to thetap of a potentiometer 110 connected between a source of negative voltage and ground. The potentiometer 110 is provided forinitial alignment of the system. 7

The emitter of the transistor 104 is also connected to the inverting input of a differential amplifier 112, which has a feed-back capacitor 114 interconnecting its output with its input, so that the amplifier 112 functions as an integrator to produce an increasing ramp voltage whenever the transistor 104 is cut off. The slope of the ramp is dependent on the capacitance of the capacitor 114 and the resistance value of the resistor 108, which is very large in relation to the resistance of the potentiometer 110, so that the latter has no effect on the slope of the ramp, but affects only the average voltage level of the ramp waveform.

The positive pulses furnished by the monostable multivibrator 102 serve to drive the transistor 104 into saturation, serving to charge the capacitor 114 through the resistor 106. The value of the resistor 106 is smaller than that of the resistor 108, so the capacitor is charged very quickly, and reaches the same level of charge by the end of each input pulse from the monostable multivibrator. After the end of each input pulse, the capacitor 114 discharges through the resistor 108, serving to produce the ramp waveform at the output of the amplifier 112. i

Each ramp begins-at theend of a pulse produced by the multivibrator, so that the phase of the ramp signal is approximately the same as that of the ac. signal ap plied to the input 62, differing therefrom only by the constant width of the pulses produced by the multivibrator 102.

The ramp signal produced at the output of the amplifler 112 is summed with the dc. signal produced at the output of the amplifier by a summing network including a resistor 116 connected from the output of the amplifier 90 to the point 118, and a resistor 120 connecting the output of the amplifier 112 to the point 118. As a result, the point 118 is provided with a ramp signal having a phase dependent upon the phase of the input signal from the tracer head 10, and a level dependent on the amplitude of the tracer head signal and also dependent on the voltage level selected by the potentiometer 96.

The point 1 18 is connected to the input of a differential amplifier 122, provided with a feedback network 124 including a resistor 126 and, connected in parallel therewith, a series circuit including a resistor 128 and a capacitor 130. The amplifier 122 functions as a line receiver to produce a positive going pulse whenever the instantaneous voltage level of the signal present at the point 118 is above a threshold potential (i.e. ground potential). This is dependent on both the phase of the ramp function, and on its average d.c. level, and so a train of pulses of variable duration is produced at the output of the amplifier 122, one for each ramp, and having a leading edge which occurs at a time position which is a linear function of the phase of the ramp, provided the deflection magnitude is constant, for any setting of the potentiometer 96. The potentiometer 110 is initially adjusted to cause such pulses to be, produced at a predetermined time in each cycle when the deflection angle is zero.

The output of the amplifier 122 is connected through a resistor 132 to the input of'an amplifier 134, the output of which is connected to one input of a flip-flop 136. The amplifier 134 functions as a line receiver and adjusts the level of the signal produced by the amplifier 122 to the value required by the flip-flop 136.

The other input of the flip-flop is connected by a line 138 to the clock generator 56 (FIG. 5B), so that the flip-flop produces on an output line 140 pulses which are synchronized with the clock pulses of the clock generator 56. The line 140 is connected to the input of a monostable multivibrator 142, which serves to generate a short pulse of standard length on an output line 144, at the leading edge of each positive going pulse on the line 140.

The line 144 is connected to the enabling input of each of a plurality of gates 146 (FIG. 5B). The block 146 contains 9 individual gates, each of which serve to connect a single input to a single output when the line 144 is energized, so that a signal present at the input of a gate at that instant is conveyed to its output.

The clock generator 56 is connected by a line 154 through a frequency divider 156 which divides the pulse repetition rate of the clock generator 56 by a factor such that there are produced on a line 158 connected to the output of the divider 156 a pulse train having a pulse repetition rate approximately 512 times the frequency of the exciting signal applied to the tracer head 10, which is also 512 times the pulse repetition rate of the pulse train appearing on the line 144.

The line 158 is connected to the input of a counter 160 which is a nine stage binary counter and therefore has 512 states. The counter 160 cycles successively through each of its 512 states, each cycling representing one cycle of the energizing frequency applied to the tracer head 10, and which correspond to one rotation around the circle illustrated in FIG. 3, through all four quadrants in succession. The time of occurrence of each pulse on the line 144 during each cycle of the counter 160, determines the deflection angle and at this moment the content of the counter 160 is gated through the gates 122 to the inputs of a group of exclusive OR gates 162, one of which is provided for the output of each stage of the counter 160. A second input of each of the exclusive OR gates 162 is connected to the eighth position of the counter 160 which is the second most significant digit thereof. The counter 160 is kept in synchronism with the exciting voltage produced by the source 9, by means of a line receiver 146 connected to the output of the source 9, the output of which is connected to the input of a monostable multivibrator 148. The output of the multivibrator 148 is a pulse at each positive-going zero crossing of the output of the source 9, and it is applied over a line 150 to a reset input of the counter 160. Accordingly, the counter 160 is reset to zero at the beginning of each cycle.

Each of the exclusive OR gates 162 receives a second input from the eighth order of the counter 160 through a gate 162. The outputs of the OR gates 162 therefore complement the pulses supplied to them from the counter 160 when an output pulse is present at the eighth output of the counter 160, and pass the pulses in uncomplemented form when no output pulse is present at the eighth output of the counter 160. With reference to FIG. 3 it is seen that the eighth position of the counter (which corresponds to the second highest order of the digital signal) is present when the deflection angle is in the second or fourth quadrants. In these quadrants it is necessary that the angle be complemented before extracting the sine of the angle, as the storage device stores only values for the first quadrant. In the second quadrant, which contains angles between 90 and 180, the sine of an angle B is equal to the sine of the angle (90-8) in the first quadrant. Similarly in the fourth quadrant, which contains angles between 270 and 360 the absolute value of the sine is equal to the sine of (90-8) in the first quadrant. The angle (90-8) is the complement of the angle B. Therefore, in the second and fourth quadrants the angle represented by the seven lowest orders of the counter 160 is complemented by the exclusive OR gates 162 before it is employed to extract the sine of that angle. The signs of the trigonometric functions are unambigious because of two additional outputs which are provided as the highest order outputs of the counter 160. An exclusive OR gate 164 has its inputs connected to the two highest order outputs of the counter 160 through the gates 146, so that the output of the gate 164 is high whenever the deflection angle is in the second and third quadrants, indicating that the cosine function is negative. An inverter 166 is connected to the highest order output of the counter 160 through a gate 146 to produce an output whenever the deflection angle is in the first and second quadrants, indicating that the sign of the sine is positive. The gate 164 and the inverter 166 are connected respectively to terminals 168 and 170, which furnish the information needed by the servo system as to the signs of the trigonometric functions. If a high value is required when the cosine is positive, an inverter may be employed in series with the output 168. Similarly, if a high value is required when the sine is negative, the inverter 166 may be omitted.

The outputs of all of the exclusive OR gates 162 are connected to the seven inputs of a read-only memory ROM 172, which is adapted to produce on a plurality of output lines 174 a digital signal representative of the sine of the angle represented by the digital signal applied to the inputs of the ROM 172 from the gates 162.

The gates 162 are also connected individually through a plurality of inverters 176 to the seven inputs of a second ROM 178. Inverting the signals produced at the outputs of the gates 162 produces a digital signal representative of an angle which is equal to less the angle represented by the outputs of the gates 162. Therefore, the ROM 148 produces on a plurality of outputs 180 a digital signal representative of the cosine of the deflection angle.

Reference to FIG. 4, where the sine and cosine functions are illustrated, will indicate that the cosine of an angle 0 is equal to sine of (90- 6 The output lines 174 are connected to inputs of a binary multimplier 182 which has another input connected from a line 184. The line 184 is provided with a pulse train having a pulse repetition rate corresponding to the speed of travel desired to be maintained by the machine. The function of the binary multiplier 182 is to provide, on an output line 186 thereof, a pulse train having a pulse repetition rate which is proportional to the product of the pulse repetition rate of the train on the line 184 and the quantity represented by the digital signal supplied to the multiplier 182 over the lines 174. Accordingly, the pulse repetition rate of the pulse train on the line 186 is A cos 0, where A is the desired speed and 0 is the deflection angle, the product being equal to the desired speed of machine movement in a first orthogonal direction. In similar fashion the 7 output lines 180 are connected to the inputs of a binary multiplier 188 which is identical to the binary multiplier 182. The multiplier 182 is also connected with the line 184 to produce a pulse train on an output line 190. Accordingly, the pulse repetition rate of the pulse train on the line 190 is proportional to A cos 0, where A is the desired speed and 0 is the deflection angle, the product being equal to the desired speed in a second orthogonal direction. The output lines 186 and 190 are connected to the line 14 and 16 of the system of FIG. 1. From the foregoing it is appreciated that the apparatus of the present invention is adapted to produce digital pulse trains in response to the output of the tracer head 10, the pulse trains each having a pulse for each increment of movement desired for the machine drive in either of two orthogonal directions. The apparatus of the present invention is not subject to drift, and is stable for an indefinite period of time.

The significance of summing a signal proportional to the magnitude of the a.c. signal present at the terminal 62 with the ramp signal generated by the amplifier 112 is to cause the deflection magnitude to have an effect upon the signal processed by the apparatus of FIG. 5. If the deflection magnitude increases, that changes the combined signal level and brings about a shift of phase of the output of the amplifier 122, with the result that the direction of the deflection represented by the output of the counter 160 is shifted by a slight angle. The direction of the shift of the output of the counter 160 is such as to modify the direction of the machine drive, so that instead of moving the stylus in a direction tangent to the surface of the pattern contacted thereby, the machine drive brings about a relative motion between the pattern and stylus in order to restore the deflection magnitude to the proper amount. Adjustment of the potentiometer 96 is effective to select the magnitude desired for the deflection of the stylus.

The pulse train on the line 184, which corresponds to the line 46 in FIG. 1 is derived from the clock generator 56 by means of a divider unit 192, which divides the pulse repetition rate of the clock generator by a convenient factor such as 180, and furnishes its output to a binary multiplier 196. The multiplier 196 is identical to the multipliers 182 and 188, and serves to produce a pulse train on a line 202 which has a repetition rate equal to the product of the rate produced by the divider 192 and a quantity represented by the setting of switches 60, which switches are connected to inputs of the multiplier 196. Accordingly, the switches 60 select the pulse rate for the train of pulses on the line 202, which is directly connected to the line 184 through a switch 204 in one of its positions. In its other position, the switch 204 connects the line 202 to the line 184 through a further divider 206, which functions to divide the pulse rate by a factor of ten. Thus the switch 204 is operative to increase the range of adjustment of the pulse rate on the line 184 by a factor of ten.

In one embodiment of the present invention, the following components were used for the indicated parts of FIG.

line receiver 98, 134 and 146 N8Tl6A multivibrators I02, I42 and 148 SN74123N flip-flop I36 SN7474N resistors 68 22K 74 100K 76 47K 88 100K 92 100K 94 100K 96 2K 106 1K 108 20K 116 47K 120 200K I26 1 Meg. capacitors 69 510 pfd 86 i .047 mfd 1 I4 I I .05 mfd multipliers l82, I84 and I96 SN7497N ROMs I72 and 178 S8771 What is claimed is:

l. A digital tracer adapted to derive a digital signal from a tracer head in response to the deflection angle of the stylus of said tracer head, comprising in combination; means for deriving a pulse occurring at a time in each cycle of the excitation of said tracer head corresponding to the direction of deflection of said stylus, means for converting the time position of said pulse within said cycle into a digital signal representative of the deflection angle, means for producing a trigonometric quantity in response to said angle, and multiplier means for producing an output pulse train representative of the product of said trigonometric function and a manually selected amplitude function.

2. Apparatus according to claim 1 including means for selecting a predetermined pulse repetition rate as an input to said multiplier means, said selecting means comprising a binary multiplier connected to a source of control pulses and to a plurality of switches for furnishing an output pulse train having a pulse repetition rate proportional to the product of the pulse repetition rate of said control pulses and a quantity represented by the position of said switches, and means for connecting the output of said binary multiplier to the input of said multiplier means.

3. Apparatus according to claim 1 including means for sensing the quadrant of said deflection angle, and means for complementing said binary representation when said deflection angle is in the second and fourth quadrants.

4. Apparatus according to claim 1, including means for producing a second trigonometric quantity in re sponse to said angle, and second multiplier means for producing a second output pulse train representative of the product of said second trigonometric function and said manually selected amplitude function.

5. Apparatus according to claim 4, wherein said means for producing a second trigonometric quantity comprises means for producing a signal representative of the complement of said angle, and means for producing a trigonometric quantity in response thereto which is the same trigonometric function as the first said trigonometric quantity.

6. Apparatus according to claim 1, wherein said means for deriving said pulse comprises means for converting the output signal of said tracer head into a pulse train with the leading edge of each pulse bearing a phase relation to said output signal in proportion to said deflection angle.

7. Apparatus according to claim 6 including means for producing a repetitive signal in response to said output signal, said repetitive signal having a sloping waveform, and means for generating said pulse train in response to a predetermined level traversed by said sloping waveform.

8. Apparatus according to claim 7, including manually operable means for controlling the average level of said sloping waveform.

9. In a tracer mechanism adapted to be employed with a tracer head having a source of an ac. exciting signal and means for producing an output signal having an amplitude proportional to the magnitude of deflection of the stylus of said tracer, and a phase relative to said a.c. signal proportional to the angle of the direction of deflection of said stylus, the combination comprising; means for producing a first signal representative of the phase of said output signal, means for producing a second signal representative of the magnitude of deflection of said stylus, means for mixing said first and second signals together to form a composite signal, and means responsive to said composite signal for deriving drive signals adapted to control the drive of said tracer mechanism for simultaneous movement in two orthogonal directions, said last named means being responsive to said composite signal for deriving drive signals adpated to control said tracer drive for movement in a direction which is responsive to said second signal.

10. Apparatus according to claim 9, including means for generating a repetitive ramp signal in response to said output signal, means for deriving a d.c. voltage in proportion to the magnitude of said deflection, means for summing said ramp signal and said d.c. voltage to produce a composite signal, and means responsive to the transition of said composite signal through a predetermined level for producing said drive signals. 

1. A digital tracer adapted to derive a digital signal from a tracer head in response to the deflection angle of the stylus of said tracer head, comprising in combination; means for deriving a pulse occurring at a time in each cycle of the excitation of said tracer head corresponding to the direction of deflection of said stylus, means for converting the time position of said pulse within said cycle into a digital signal representative of the deflection angle, means for producing a trigonometric quantity in response to said angle, and multiplier means for producing an output pulse train representative of the product of said trigonometric function and a manually selected amplitude function.
 2. Apparatus according to claim 1 including means for selecting a predetermined pulse repetition rate as an input to said multiplier means, said selecting means comprising a binary multiplier connected to a source of control pulses and to a plurality of switches for furnishing an output pulse train having a pulse repetition rate proportional to the product of the pulse repetition rate of said control pulses and a quantity represented by the position of said switches, and means for connecting the output of said binary multiplier to the input of said multiplier means.
 3. Apparatus according to claim 1 including means for sensing the quadrant of said deflection angle, and means for complementing said binary representation when said deflection angle is in the second and fourth quadrants.
 4. Apparatus according to claim 1, including means for producing a second trigonometric quantity in response to said angle, and second multiplier means for producing a second output pulse train representative of the product of said second trigonometric function and said manually selected amplitude function.
 5. Apparatus according to claim 4, wherein said means for producing a second trigonometric quantity comprises means for producing a signal representative of the complement of said angle, and means for producing a trigonometric quantity in response thereto which is the same trigonometric function as the first said trigonometric quantity.
 6. Apparatus according to claim 1, wherein said means for deriving said pulse comprises means for converting the output signal of said tracer head into a pulse train with the leading edge of each pulse bearing a phase relation to said output signal in proportion to said deflection angle.
 7. Apparatus according to claim 6 including means for producing a repetitive signal in response to said output signal, said repetitive signal having a sloping waveform, and means for generating said pulse train in response to a predetermined level traversed by said sloping waveform.
 8. Apparatus according to claim 7, including manually operable means for controlling the average level of said sloping waveform.
 9. In a tracer mechanism adapted to be employed with a tracer head having a source of an a.c. exciting signal and means for producing an output signal having an amplitude proportional to the magnitude of deflection of the stylus of said tracer, and a phase relative to said a.c. signal proportional to the angle of the direction of deflection of said stylus, the combination comprising; means for producing a first signal representative of the phase of said output signal, means for producing a second signal representative of the magnitude of deflection of said stylus, means for mixing said first and second signals together to form a composite signal, and means responsive to said composite signal for deriving drive signals adapted to control the drive of said tracer mechanism for simultaneous movement in two orthogonal directions, said last named means being responsive to said composite signal for deriving drive signals adpated to control said tracer drive for movement in a direction which is responsive to said second signal.
 10. Apparatus according to claim 9, including means for generating a repetitive ramp signal in response to said output signal, means for deriving a d.c. voltage in proportion to the magnitude of said deflection, means for summing said ramp signal and said d.c. voltage to produce a composite signal, and means responsive to the transition of said composite signal through a predetermined level for producing said drive signals. 